LookOut is a plugin which allows Thunderbird to interface with Microsoft's mail tools by decoding metadata and attachments encapsulated/embedded in a TNEF encoded attachment (aka winmail.dat).Support: Thunderbird and SeaMonkey

DOM Inspector is a tool that can be used to inspect and edit the live DOM of any web document or XUL application. The DOM can be navigated using a two-paned window displaying a variety of different views on the document and all nodes within.

SmartTemplate4 offers an easy way to automatically create customized replies by auto-inserting various mail headers. Templates can be created for every account as well as for the default (all email accounts). Also supports the Stationery Add-on.